This invention relates to an apparatus and method for controlling a hybrid vehicle having an internal combustion engine as a primary mover and a secondary mover which incorporates an energy storage device.
It is known to provide a vehicle with a secondary source of motive power. Such secondary sources of motive power can comprise a rechargeable battery and electric motor combination or a flywheel, for example. This invention has particular application to a flywheel hybrid vehicle but is not limited thereto.
SAE technical paper 2008-01-0083, Apr. 14-17, 2008, describes an arrangement consisting of a continuously variable transmission (CVT) connected between the engine and gearbox of a vehicle and configured to drive a flywheel through a gearset. The arrangement can add or subtract power to that supplied by the engine.
In a flywheel-based energy storage and recovery system, manipulation of the CVT ratio achieves control of energy storage and recovery. When the ratio is set so as to speed up the flywheel, energy is stored and when the ratio is set so as to slow down the flywheel, energy is recovered.
A road car is capable of very high power transfer during braking and the key to hybrid system effectiveness is capturing as much of this (normally wasted) energy as possible. However, vehicle retardation is additionally caused by needing to overcome the pumping losses from motoring the engine during such retardation. Typically the degree of this retardation is greater for a gasoline engine, compared with a diesel engine, as during braking the intake throttle is almost completely shut. Therefore, pumping losses can be significant. As a consequence of motoring the engine, the amount of available energy to transfer to a flywheel or other energy storage device is diminished, and less than the overall kinetic energy of the vehicle. In short, because of the need to overcome pumping work, the available energy to be stored is less than ideal.